``` BIN 00010000 BIN 00100010 BIN 01111110 BIN 00000000 ``` (If you know about binary numbers, then it should help you to know that **BIN** is used to write a number in binary instead of the usual decimal.) These eight numbers are stored in memory, in eight places, each of which has an address. The address of the first byte, or group of eight digits, is **USR "S"** (**S** because that is what we chose in (ii)), that of the second is **USR "S"+1**, and so on up to the eighth, which has address **USR "S"+7**. **USR** here is a function to convert a string argument into the address of the first byte in memory for the corresponding *user-defined graphic*. The string argument must be a single character which can be either the user-defined graphic itself or the corresponding letter (in upper or lower case). There is another use for **USR**, when its argument is a number, which will be dealt with in subsequent chapters. Even if you don't understand this, the following program will do it for you: ``` 5 FOR n=0 TO 7 10 READ row: POKE USR "S"+n,row 15 NEXT n 20 DATA BIN 00000000 25 DATA BIN 01111100 30 DATA BIN 00100010 35 DATA BIN 00010000 40 DATA BIN 00010000 45 DATA BIN 00100010 50 DATA BIN 01111110 60 DATA BIN 00000000 ``` The above example can also be rewritten using integer variables without the use of **BIN** while still expressing the graphic matrix in binary form. Can you restate it per what you've learned? ### POKE and PEEK The **POKE** statement stores a number directly in a memory location, bypassing the assignment (**LET**) mechanism normally used by *NextBASIC* which also tracks its place in memory. The opposite of **POKE** is **PEEK**, and this allows us to look at the contents of a memory location although it does not actually alter the contents of that location. They will be dealt with properly in *Chapter 23*.There are a few more efficient ways to type all the above but for now, we're using the simplest forms of **PEEK** and **POKE.** The tokens (which we referred to a little earlier) are stored right after character code **128.** As you saw, in the character set printing example, codes **0** to **31** were absent. These are *control* characters or as commonly referred to: *control codes*. They either don't produce characters on screen – although they do have an effect on what's printed there – or, alternatively, they are used to control something other than the display itself, and the screen displays ? to show that it doesn't understand them. They are described more fully in *Appendix A*.